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  Java Practices -> Know the core libraries
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<div class='page-title'>Know the core libraries</div>

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<br>Java differs from other languages in that the number of classes and
interfaces in its standard libraries is very large. Many common tasks have
already been implemented by these libraries. 

<P>Advice to beginners might include :
<ul>
<li>the most widely used packages are 
<tt><a href='http://java.sun.com/javase/6/docs/api/java/lang/package-summary.html'>java.lang</a></tt> and 
<tt><a href='http://java.sun.com/javase/6/docs/api/java/util/package-summary.html'>java.util</a></tt>.
<li>for working with data, see 
<tt><a href='http://java.sun.com/javase/6/docs/api/java/sql/package-summary.html'>java.sql</a></tt>,
<tt><a href='http://java.sun.com/javase/6/docs/api/javax/sql/package-summary.html'>javax.sql</a></tt>,
and 
<tt><a href='http://java.sun.com/javase/6/docs/api/java/io/package-summary.html'>java.io</a></tt>. 
<li>for graphical applications, see the Swing classes 
(<a href='http://java.sun.com/javase/6/docs/api/javax/swing/package-summary.html'>javax.swing</a>, and so on). 
<li>for server applications, see the 
<a href='http://java.sun.com/products/servlet/2.5/docs/servlet-2_5-mr2/index.html'>servlet</a> and 
Java Server Page APIs.
<li>for other packages, you should skim through their documentation just to get an 
idea of what is available. Later, when a specific need arises, you will often know 
which packages might be helpful.
<li>do not be too intimidated by the large number of classes.
Some are used often, but most are used relatively rarely.
</ul>

<p>As well, the standard JDK libraries :
<ul>
<li>are generally of high quality</li>

<li>
often improve their performance over time</li>

<li>
are widely used, and usually form <em>defacto</em> standards</li>
</ul>
Implementing something which already exists in the libraries is probably
wasted effort.
<p>Significant changes and additions to the standard libraries occur in
each major release, and it pays to keep current. For example, the 1.4 release
of the JDK includes regular expressions, assertions, logging services,
and more, in its list of <a href="http://java.sun.com/j2se/1.4.2/docs/relnotes/features.html">new
features</a>. The Java 5 release has several major <a href="http://java.sun.com/j2se/1.5.0/docs/relnotes/features.html">new
features</a>, including generics, an enhanced for loop, enums, autoboxing, and annotations.
The Java 6 release has no new language features, and is not as dramatic as the 1.5, 
but it still has some interesting <a href="http://java.sun.com/javase/6/webnotes/features.html">new features</a>, 
such as scripting, the 
<a href="http://java.sun.com/javase/6/docs/technotes/tools/index.html#jconsole">JConsole</a> 
monitoring tool, and various Swing improvements.
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